Method and apparatus for electrostatic spraying



June 19, 1962 H. J. REINDL 3,039,890

METHOD AND APPARATUS FOR ELECTROSTATIC SPRAYING Filed July 10, 1958 2 Sheets-Sheet 1 I M M INVENT OR. 9 3 Harold .1. Remdl.

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His Attorney.

2 Sheets-Sheet 2 Power Source INVENTOR. Harold J. Re/ndl.

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H. J. RElNDL METHOD AND APPARATUS FOR ELECTROSTATIC SPRAYING Filed July 10, 1958 United 3,039,890 METHOD AND APPARATUS FOR ELECTROSTATIC SPRAYING Harold J. Reindl, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed July 10, 1958, Ser. No. 747,681 9 Claims. (Cl. 117-93) This invention relates to electrostatic coating operations and is particularly concerned with devices and methods for operating said devices whereby greater efliciency is obtained.

The use of rotating devices as a means for aiding in the distribution of coating materials, such as paint, is rather well developed, particularly where the device forms one pole of an electrostatic circuit so that paint centrifugally thrown therefrom is charged and is thereby attracted to an article to be painted space-d from the device and carrying the opposite charge. These rotating devices, which may be termed centrifugal distributors, take the form of discs, cones, blades, etc., all of which have as one of their basic functions, centrifugal distribution of the paint therefrom whereby, when the device is rotating at a sufiiciently high speed, paint supplied adjacent the center thereof will be centri'fugally distributed over the surface of the device and will be thrown from the edge thereof. When the device is electrostatically charged, electrostatic forces tend to break up and atomize the paint as it leaves the edge and simultaneously charge the atomized particles.

The present invention is directed to a rotating centrifugal coating distributor to be used in conjunction with electrostatic forces wherein the efficiency of the device is improved and the electrostatic charge induced on each particle of paint is increased markedly due to the specific structure of the distributor.

It is, therefore, an object of this invention to improve the efficiency of electrostatic coating operations when using centrifugal distributors and, in carrying out this object, it is a further object to concentrate the electrostatic forces at a plurality of spaced distribution points around the periphery of a distributor whereby the efficiency thereof is increased.

it is a further object of the invention to improve the centrifugal dispersion of the coating material during the distribution thereof and, to this end, the present invention utilizes a device having a. plurality of distributing points circumferentially spaced around the periphery of a central shaft which causes the entire device to rotate.

In carrying out the above object, it is a further object of the invention to provide a brush formed from bristles made of any suitable material, metallic or nonmetallic, which brush has means adjacent the center thereof for receiving coating material which can be centrifugally distributed onto the bristles and thereafter caused to flow along the bristles until it is discharged therefrom at the ends thereof. Each bristle being charged concentrates the electrostatic charge at the end thereof whereby the coating material which is thrown therefrom receives a high and concentrated electrostatic charge.

Another object of the invention is to vary the density of the bristles as required to accomplish desired results, for example, the bristles may be formed into a brush ten to twenty bristles thick or the bristles may be distributed in a line only one bristle deep. In other embodiments, the bristles may be graduated so that coating material coming from the end of one bristle feeds at least in part onto a contiguous portion of an adjacent longer bristle until it is finally centrifugally discharged from the longest bristle.

Another object of the invention is to vary the voltage in connection with the electrostatic charge in accordance with the number of bristles used whereby relatively lower voltages are possible when using brushes having a relatively small number of bristles.

In carrying out this object, it is a concurrent object to vary the density of coating material deposition by varying the number of bristles used.

A still further object of the invention is to control the field of electrostatic coating by controlling the shape of the brush and number of bristles therein.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIGURE 1 shows one form of the invention wherein the brush is relatively thick and includes a plurality of layers of bristles, all of which have substantially the same length.

FIGURE 2 is a fragmentary view showing a modification of the device shown in FIGURE 1.

FIGURE 3 i a modification of the device shown in FIGURE 1 wherein the bristles are graduated in length from the lower portion of the brush to the upper portion of the brush.

FIGURE 4 is still another embodiment of the device wherein the brush includes only one row of bristles.

FIGURE 5 is a sectional view of the device shown in FIGURE 4.

FIGURE 6 is a fragmentary enlarged section of a portion of the periphery of the cup used in the brush shown in FIGURE 4 showing how the bristles are attached there- FIGURE 7 is a diagrammatic view showing the distributor in the center of a noncircular conveyor wherein articles to be coated are moved around the distributor and then out of the field of spray thereof.

In my copending application, S.N. 687,107, and now U.S. Patent No. 2,975,755, I have shown a centrifugal type distributor wherein a noncircular blade is used as a means for distributing paint onto surfaces to be painted. In this connection, the distribution has a pulsating effect due to the noncircular shape of the distributor whereby paint is applied in waves. -In my copending application,

- S.N. 710,665, and now US. Patent No. 2,976,175, an-

other distributor of the centrifugal type is shown wherein a squirrel-cage is used as a means for distributing the paint. In my copending application, S.N. 717,673, and now US. Patent No. 2,975,757, still another method of distributing paint is disclosed wherein paint is atomized directly onto the surfaces of rotating distributing means whence it picks up a charge and is mechanically and electrostatically directed to the article to be painted. In all of these disclosures, the pattern of painting may he arrived at by proper design and operation of the distributor.

In all prior art distributors, relatively high voltages are used in order to properly charge the particles of paint as they leave the distributor and, in all of these prior systems, the charge is induced in the paint as it leaves an extended edge of the distributor. I have found that the charge can be increased by concentrating the flow of current at a point whereby similar distribution results can be obtained and, in some instances, wherein the voltages used may be reduced due to the fact that the area of charging surface is less due to the concentration thereof at a point rather than over an extended surface.

The present invention is directed to a means for utilizing this principle in connection with centrifugal distributors whereby lower voltages may generally be used and wherein a highly eflicient distributing device is provided which combines the electrostatic principle of point discharge with the centrifugal principie of fluid distribution.

This is accomplished by using a centrifugal distributor made in the form of a brush including a plurality of bristles or fingers attached to a central distributing device wherein the brush is rotated at relatively high speeds in the order of 1500 to 3000 r.p.m., for example, and wherein liquid paint or other coating material is supplied adjacent the center thereof which paint is centrifugally fed to the bristles whence it moves along the surface of the bristles to the ends thereof and is then centrifugally thrown outwardly in expanding circular pattern and is simultaneously electrostatically charged and broken up into a very fine mist.

Referring specifically to FIGURE 1, one embodiment of the invention is shown wherein a multiple layer brush 20 is used having either metallic or nonmetallic bristles 22. In this instance, the brush includes brass bristles although nylon, animal bristles or steel or nickel bristles, etc., may be used effectively. The bristles 22 are carried by a central hub 24 which comprises a shell-like metal cup member that is attached to a shaft 26 driven by a motor, not shown. The motor may be electrically or air driven as desired. A stationary housing 28 which surrounds the shaft 26 supports a paint supply tube 30 which drips paint supplied thereto onto the interior surface of the hub 24, preferably adjacent the bottom thereof. The sheet metal hub 24 is curved outwardly from the bottom and the bristles are fixed in the walls thereof preferably with apertures therebetween so that paint centrifugally distributed on the sides of the hub will pass through the apertures and onto the bristles and will be centrifugally fed outwardly thereof until the ends are reached whence it will be thrown from the bristles of the brush. Any other suitable means for feeding and attachment may be used. The shaft 26 is connected to one side of a power source 32, the other side being connected to the article 34 to be painted. Thus, the bristles act as electrodes emanating radially outwardly from a common center and, as the paint leaves the ends thereof, it is charged and electrostatically atomized and dispersed into minute particles and these mist-like particles are attracted to the article 34 due to the opposite charge thereon. Paint is supplied to the tube 30 from a source not shown by means of gravity or a pump as desired.

If desired, the paint may be fed into an auxiliary cup 31 shown in FIGURE 2 secured to the housing wherein the tube is maintained below the top of the cup. This permits shut-downs without cleaning the lines as noted in my copending application, S.N. 696,777, and now US. Patent No. 2,899,136.

FIGURE 3 shows another embodiment of the invention wherein the bristles are graduated from the bottom to the top thereof with respect to length. In this connection, paint is fed to the lower bristles only and tends to migrate upwardly through the brush and pass from one layer of bristles to the next until it is finally discharged from the longest bristles adjacent the top of the brush. This embodiment does not cover as wide a field of painting and is useful in connection with certain operations where con trol is required.

In FIGURE 4, another embodiment is shown wherein a central cup 40 carries a single layer brush .2 thereon. The brush 42 is made up of a plurality of bristles 44 which may be U-shaped as shown in FIGURE 6 passing through apertures in the cup or hub 40. In between each pair of bristles are apertures 46 which act as paint feeding means and paint being centrifugally thrown from these apertures immediately impinges on the bristles 44 whereupon the centrifugal action of feeding the paint along the bristles to the ends thereof progresses. In this connection, it should be understood that FIGURE 6 is greatly enlarged and the bristles .4 are substantially contiguous to one another in the actual device so that paint passing through the apertures 46 impinges directly upon the bristles. If the bristles are spaced more widely, the

apertures 46 may be angled so that the paint is thrown directly onto the bristles, or the apertures which hold the 4 l bristles may be enlarged so that paint may pass therethrough directly onto the bristles. It is understood that the bristles in the other two embodiments may be attached to the hub in the same manner. In all other respects, the embodiment shown in FIGURE 4 is similar to those shown in FIGURES 1 and 3. However, due to the fact that the brush is only one bristle thick, the field of painting is much narrower and this can be used to advantage with respect to specific articles to be painted. It is to be understood that similar brushes having two layers, three layers of bristles, or ad infinitum, may be used; in these cases, the bristles in each row are preferably staggered with respect to adjacent rows to improve the paint distribution. In these instances, the several layers may be alternated with respect to the feeding apertures to improve the coating of the bristles with paint.

In FIGURE 7, the centrifugal device 20 is shown at the center of a conveyor 50 which is shown diagrammatically. A plurality of articles 52 to be painted pass therearound in the direction of the arrows. The conveyor system as shown in FIGURE 7 is fully disclosed in my copending application, S.N. 698,490, and now -U.S. Patent No. 2,947,281. It is understood, of course, that the articles 5 2 are connected to one side of a power source while the distributor 20 is connected to the other side thereof.

In practice, the greater the number of bristles used, the greater the voltage required and, in connection with a brass brush three-eighths of an inch thick and six inches in diameter, having bristles .006" in diameter, I prefer to use voltages in the order of 100,000 volts and rotate the brush at 2000 r.p.m. The article to be painted is located eighteen inches away. Where the brush is reduced in thickness, the voltage may be reduced. However, in all instances, the specific voltage, speed and spacing to be used is best arrived at by trial so that proper electrostatic charging, atomizing and deposition of the particles is obtained.

1 have found that the use of a brush type distributor improves the efiiciency of the coating apparatus since the particles are more fully charged and, therefore, are more fully attracted to the target or article to be painted. Similarly, it is quite apparent that the voltage required for specific coating operations may be reduced where brush type distributors having a greatly reduced number of bristles are used and this makes the structure more flexible and, therefore, more useful.

To control the field of painting, shields may be used which are charged the same as the distributor. This type of control is shown fully in my copending application, S.N. 726,450.

While the embodiments of the present invention as herein disclosed constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In a method for distributing liquid coating from a plurality of separated and elongated electrodes emanating radially outwardly from a common central hub, the steps comprising; supplying liquid coating material to a central distributing zone, rotating the supply of liquid coating material in said zone to centrifugally distribute the same as a radially expanding uniform thickness film outwardly from said zone while simultaneously feeding liquid coating material to said zone for replenishing that which is distributed therefrom, dividing said expanding film into a plurality of separate supported film paths, each spaced from the other in a generally radially expanding pattern, simultaneously rotating said separate film paths for progressively centrifugally throwing liquid coating material making up said film paths outwardly and away from their supports, and simultaneously electrostatically charging the unsupported liquid coating material for dispersing the same and for causing deposition of the dispersed and charged material upon an object bearing an opposite charge and spaced from said supported film paths.

2. In a method for electrostatically depositing paint from a central distributing source, the steps comprising; supplying liquid paint to a central distributing zone, rotating the supply of paint in said zone at a speed sufficient to centrifugally distribute the same in a thin expanding film of uniform depth radially outwardly from the zone while simultaneously replenishing the paint distributed therefrom, dividing said film into a plurality of separate supported film paths, each radially spaced from the other, while simultaneously rotating said separate film paths for centrifugally throwing paint making up the separate film paths outwardly and away from their supports, and electrostatically charging the paint as it passes from the support and simultaneously dispersing the paint in the form of particles and causing deposition of the dispersed charged particles of paint onto an object to be painted which bears an opposite charge to the charge carried by said dispersed and charged paint particles.

3. In an electrostatic painting apparatus for use in painting an article spaced therefrom, the combination comprising; a brush-like structure including a central distributing means consisting of a cup-like hub including a vertical wall, a paint supply tube for supplying liquid paint to said cup-like hub, a plurality of horizontally disposed and elongated bristles carried by said hub wall and emanating radially outwardly therefrom in generally equally spaced relation entirely around said hub, said hub wall including apertures therethrough adjacent said bristles through which the liquid paint, contained within the cup, may flow outwardly onto the base of said bristles, driving means for rotating the hub and brush at a speed to create sufiicient centrifugal force to cause paint in said hub to flow outwardly of said apertures and onto said bristles and to thereafter cause said paint to flow outwardly along said bristles, a power source connected to said brush-like structure at one electrical connection thereof and adapted to 'be connected to the article to be painted at the other connection thereof whereby paint is centrifugally thrown from said bristles in dispersed form and wherein the particles in said dispersion are electrostatically charged with an opposite charge to the charge on said article and are thereby attracted thereto.

4. The apparatus as claimed in claim 3 wherein the bristles are nonmetallic.

5. The apparatus as claimed in claim 3 wherein the bristles are metallic.

6. The apparatus as claimed in claim 3 wherein the bristles are disposed in a plane whereby the brush is substantially only one bristle thick.

7. In an electrostatic painting apparatus for use in painting an article spaced therefrom, the combination comprising; a brush-like distributor including a central cup-like supply hub including a vertical wall, paint supply means for supplying liquid paint to said hub, said hub wall including a plurality of apertures spaced around the entire periphery thereof, a plurality of generally horizontally disposed elongated wire-like electrodes extending radially outwardly from said hub and passing through at least some of said apertures, said apertures being of such a size that there is clearance around said wires so that liquid paint contained within the hub may fiow outwardly through said apertures and onto the base of said wires, driving means for rotating the hub and the wires at a speed to create sufiicient centrifugal force to cause paint from said hub to flow upwardly of the hub and outwardly of said apertures onto the base of said wires and to thereafter cause said paint to flow outwardly along said wires, a power source connected at one side thereof to the painting apparatus and connected at the other side thereof to the article to be painted whereby paint centrifugally thrown in dispersed form from said wires and wherein the particles in said dispersion are electrostatically charged with an opposite charge to the charge on the article and are thereby attracted thereto.

8. The apparatus as claimed in claim 7 wherein each pair of wires is formed from a single length of wire 'bent into hairpin form and passed through two spaced apertures.

9. The apparatus as claimed in claim 8 wherein an aperture is provided between each intermediate pair of spaced apertures and closely adjacent thereto for supplying additional paint to the wires passing through said two adjacent apertures.

References Cited in the file of this patent UNITED STATES PATENTS 1,022,956 Leng Apr. 9, 1912 1,506,226 Dock Aug. 26, 1924 1,520,446 Satake Dec. 23, 1924 1,636,949 Bassler July 26, 1927 1,753,019 Page Apr. 1, 1930 2,275,148 Hornbeck Mar. 3, 1942 2,442,206 Kempthorne May 25, 1948 2,661,984 Peebles et a1. Dec. 8, 1953 2,671,650 Jauch et a1. Mar. 9, 1954 2,685,536 Starkey et al Aug. 3, 1954 2,780,565 Juvinall Feb. 5, 1957 2,893,894 Ransburg July 7, 1959 FOREIGN PATENTS 248,254 Great Britain Mar. 4, 1926 

1. IN A METHOD FOR DISTRIBUTING LIQUID COATING FROM A PLURALITY OF SEPARATED AND ELONGATED ELECTRODES EMANATING RADICALLY OUTWARDLY FORM A COMMON CENTRAL HUB, THE STEPS COMPRISING; SUPPLYYING LIQUID COATING MATERIAL TO A CENTRAL DISTRIBUTING ZONE, ROTATING THE SUPPLY OF LIQUID COATING MATERIAL IN SAID ZONE TO CENTRIFUGALLY DISTRIBUTE THE SAME AS A RADIALLY EXPANDING UNIFORM THICKNESS FILM OUTWARDLY FROM SAID ZONE WHILE SIMULTANEOUSLY FEEDING LIQUID COATING MATERIAL TO SAID ZONE FOR REPLENISHING THAT WHICH IS DISTRIBUTING THEREFROM, DIVIDING SAID EXPANDING FILM INTO A PLURALITY OF SEPARATE SUPPORTED FILM PATHS, EACH SPACED FROM THE OTHER IN GENERALLY RADIALLY EXPANDING PATTERN, SIMULTANEOUSLY ROTATING SAID SEPARATE FILM PATHS FOR PROGRESSIVELY CENTRIFUGALLY THROWING LIQUID COATING MATERIAL MAKING UP SAID FILM PATHS OUTWARDLY AND AWAY FROM THEIR SUPPORTS, AND SIMULTANEOUSLY ELECTROSTATICALLY CHARGING THE UNSUPPORTED LIQUID COATING MATERIAL FOR DISPERSING THE SAME AND FOR CAUSING DEPOSITION OF THE DISPERSED AND CHARGED MATERIAL UPON AND OBJECT BEARING AN OPPOSITE CHARGE AND SPACED FROM SAID SUPPORTED FILM PATHS. 